AstraZeneca has signed a deal to buy the rights to Rigel's rheumatoid arthritis drug, fostamatinib disodium (R788)

The drug had previously shown positive results in separate studies however, and AZ are keen to take advantage of what would be an oral alternative to injections for RA sufferers. The current treatment market for the autoimmune inflammatory disease is estimated to be around $13bn.

The deal will see AZ make an upfront payment of $100m, with up to an additional $345m payable if certain specified milestones in development, regulation and first commercial sales are achieved.

Rigel could also receive an additional $800m of specified sales-related milestone payments if the product achieves considerable commercial success and significant royalties on net sales worldwide.

Fostamatinib disodium is the furthest developed oral Spleen Tyrosine Kinase (Syk) inhibitor being evaluated for RA. This new treatment potentially offers an alternative for patients who have failed to respond adequately to a traditional disease modifying anti-rheumatic drug (DMARD), such as methotrexate, where a TNF biologic add-on treatment would currently be considered.

The drugs are proposed to work by blocking the intracellular signalling of various immune cells implicated in the destruction of bone and cartilage which is characteristic of RA.

AZ will assume responsibility for all development, regulatory filings, manufacturing and global commercialisation activities in all licensed indications.

A phase III programme is anticipated to begin in the second half of 2010, with the goal of filing new drug applications with the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) in 2013.